This invention relates to an improvement in fabricating perforated composite laminate structure and, more particularly, but not by way of limitation, to a method of fabricating perforated composite laminate structures into predetermined contoured shapes.
The manufacture of composite laminate panels, such as acoustic surface panels, made from epoxy resin impregnated woven graphite fabric or the like requires some means for providing porosity through the panel. The drilling or piercing of holes through the panels after the sheet has been cured is costly and tends to reduce the mechanical properties of the acoustical panel system. For example, because the fibers of the reinforcing material are rigidly held in the cured sheet, drilling or punching apertures will tend to break a portion of the strands of such reinforcing material, particularly if the panel is laminated with a series of superimposed sheets. The problems are particularly acute when it is desired to contour the final panel structure is to a particular configuration.
Further, for aerospace applications it is necessary to provide complex shapes and the prior art while providing generally adequate composite acoustic sheets only provided flat panels and could not provide cured or complex curved perforated acoustic sheets.
Prior art methods of producing various forms of perforated sheet material from resin impregnated cloth material are taught by U.S. Pat. Nos. 2,289,177; 3,704,194; and 3,787,546.
U.S. Pat. No. 2,289,177 by F. J. Chandler teaches perforating partially cured flexible composite material.
U.S. Pat. No. 3,704,194 by S. C. Harrier teaches providing perforations in reinforced plastic members by first pressing a partially cured sheet, or series of sheets, over spaced apart, pointed, partially elastic, studs projecting from a mold surface portion. The sheet is then finally cured while pressed against the mold surface portion.
U.S. Pat. No. 3,787,546 by Pratt et al., teaches making a perforated resin plastic sheet on a studded mold by pressing a partially cured plastic sheet over the studs so that the studs project through the sheet. A pressure through a medium holds the sheet against the mold surface while final curing takes place.
None of the noted patents could provide curved or complex curved perforated composite sheets particularly adapted for the stringent requirements of acoustic aerospace applications.